Download Guide to Footrot in Sheep

Guide to Footrot in Sheep
By Dr. Ileana Wenger
S
heep footrot is a painful, debilitating bacterial infection of the foot that can lead to severe production
losses and increased culling of ewes. Sheep footrot is not the same as the infection that is seen
in cattle, but it can be shared with goats; therefore goats must undergo the same prevention and
control measures as sheep.
The best way to deal with sheep footrot is to avoid introducing it to your farm!
Be very cautious when you
purchase sheep, and manage the
biosecurity of your flock carefully.
If, in spite of your best efforts,
your flock does become infected,
and you find yourself with several
lame sheep, there are some basic
facts you need to know in order to
start an eradication program.
Not every lame sheep has footrot so a correct diagnosis is critical. Footrot most often affects the front feet, forcing the
animal to its knees. Sheep with infected back feet have a distinctive stance, as they try to keep their weight off their painful
toes. Infected hooves are often encased in manure, which seals in warmth and moisture the bacteria needs to thrive.
This article first appeared in the Summer 2007 issue of Sheep Canada magazine.
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Causes of Lameness in Sheep
1. Active sheep footrot requires the presence of at
least two separate bacteria in the foot:
a. Fusobacterium necrophorum is a common
bacterium found in soil and present in animal
feces.
b. Actinomyces (Corynebacterium) pyogenes is
a common bacteria in soil and is also commonly
found in foot abscesses.
c. Dichelobacter (Bacteroides) nodosus is
responsible for sheep footrot infection. It lives
in the feet of sheep, and can only survive for
seven to 14 days anywhere else. Dichelobacter
can persist for up to three years in chronically
infected hooves.
Footrot is extremely painful! It starts between the
toes then under-runs the sole, causing the sole
and the hoof wall to separate. The bacteria eats
away at the hoof tissue, causing the foul smell
associated with the disease.
2. There are three clinical causes of lameness in
sheep associated with these bacteria; they are
all related but it is important to be able to tell the
difference between them.
a. Interdigital dermatitis (between the toes),
also known as foot scald, is an early infection with
Fusobacterium. Sheep with interdigital dermatitis
have a moist, reddened, angry-looking lesion
between the toes, often with a whitish layer of
dead tissue on the surface. Lameness is usually
mild but may progress to severe in some cases. It
is generally seen during or shortly after a period
of warm, wet weather, especially in conditions
causing trauma to the feet (rocks or stubble
grazing).
b. Foot abscesses may occur when Actinomyces
invades tissue already weakened by an interdigital
infection. The sheep will be severely lame and an
abscess can be drained from the sole of the foot.
In prolonged cases the abscess may rupture and
drain from the coronary band (the area at the
top of the hoof where it meets the hair on the
sheep’s leg).
c. Footrot occurs when a carrier sheep infected
with Dichelobacter is introduced to the flock and
these very invasive bacteria infect the tissue that
has been weakened by an interdigital dermatitis.
Depending on the strain of Dichelobacter present,
it can be a mild (benign) or very severe (virulent)
infection. Sheep are often so lame they cannot
walk and are seen on their knees trying to graze.
The infection under-runs the hoof wall and sole,
causing an extremely painful separation of the
hoof from the underlying tissues.
Footrot treatment is time-consuming, expensive and
back-breaking work.
3. Once the predisposing factors of warmth
and moisture are present, the organism will
easily spread from chronically infected carrier
Footrot damage is visible from the exterior of the hoof. The foot on the left has recovered but has a permanent crease
where the hoof wall has collapsed. The middle hoof shows the dark shadow where the tissue underneath has died. The foot
on the right has also recovered but is growing erratically.
sheep to other members of the flock. All ages
and types of sheep are susceptible, although
selection for genetically resistant sheep in
countries where the disease is widespread has
helped to reduce the severity of the disease.
4. Infection does not provide natural immunity to
the disease. Young lambs may show signs of
foot scald when housed with chronically infected
ewes. Carrier sheep often have misshapen feet
and may require more frequent foot trimming.
Acute sheep footrot is usually accompanied
by a distinctive foul odour and discharge.
5. Diagnosis in severe cases is based on clinical
signs of lameness, separation of the hoof,
discharge and foul odour. In early cases
of interdigital dermatitis and less virulent
strains, samples should be submitted to a
lab by your veterinarian for confirmation.
6. Treatment of sheep footrot is time-consuming,
expensive and backbreaking work. The best
defense is to avoid bringing carrier animals
into your flock. However, if your flock does
become infected, it is not necessary to cull
the entire flock. Sheep footrot is a treatable
disease and can be eradicated from your
flock if strict protocols are diligently followed.
7. Footrot vaccines are available in some countries,
but are extremely variable in efficacy. This is due in
part to the many different strains of Dichelobacter
involved. Vaccines may help, when used in
conjunction with foot trimming and soaking, but
will not take the place of a comprehensive program
of trimming and soaking.
Protocol for Eradication of Sheep Footrot
1. Thoroughly
examine
the
feet
of
ALL
sheep in the flock. Don’t forget the rams.
2. Sheep with severely infected, misshapen or
chronically infected feet should be culled.
3. Sort the flock into two groups: those
with apparently sound, healthy feet (the
exposed group) and those that are lame
or known to be infected (the lame group).
4. Animals in the exposed group should have their
feet carefully trimmed, and be footbathed in a 20%
zinc sulfate solution according to the schedule in
Figure 1. Disinfect hoof trimmers between animals.
5. After trimming and footbathing, move the
exposed group to clean ground (no contact with
Moisture / trauma
↓
Softening, damage to skin between toes
↓
Invasion by Fusobacterium necrophorum
↓
Interdigital Dermatitis or Foot Scald
↓
Invasion by
Invasion by
Dichelorbacter nodosus
Actinomyces pyogenes
↓
↓
Foot abscess
Sheep footrot
Figure 1. Footsoaking schedule for the eradication of footrot
Week
1
2
3
4
5
6
7
8
9
Infected
Group
1 hour soak
x2
1 hour
soak
1 hour
soak
1 hour
soak
1 hour
soak
1 hour
soak
1 hour
soak
1 hour
soak
1 hour
soak
Exposed
Group
1 hour soak
x2
1 hour soak
x2
1 hour soak
x2
sheep for at least 14 days). Make sure they do
not go anywhere near the infected group or walk
on ground the infected group have walked on.
6. Trim the feet of all sheep in the infected group.
ALL feet must be trimmed and all cracks,
pockets or tracts must be dug out down to
healthy normal tissue. Disinfect hoof trimmers
between animals. We have found that a rotary
tool such as a Dremmel is indispensable for this
job. The bacteria must be exposed to air and
the foothbath solution to be killed. The rotary
tool allows this to be done easily and safely.
7. Infected sheep should be treated with a suitable
long-acting antibiotic at time of foot trimming.
8. Infected sheep must be foot soaked in a
20% zinc sulfate solution according to the
schedule in Figure 1. Ensure that sheep stand
in the bath for the full hour. The zinc sulfate is
poisonous; do not allow the sheep to drink it.
9. After each treatment, the sheep should be turned
out on to clean pasture (no contact with sheep
for at least 14 days).
10. The feet of sheep in the
infected group should
be re-examined and
re-trimmed
every
three to four weeks
during the treatment
period. Any sheep
that start or continue
to limp throughout
the treatment period
should
be
culled.
11. The flock cannot be
considered
cured
until they have been
through at least one
warm/wet
season
after the treatments
are complete.
Preparation of the Footbath
The design of the footbath will depend to a large
extent on the number of sheep to be treated. It
should be able to hold at least 10% of the flock at
one time.
Zinc sulfate monohydrate power is available from
feed and livestock supply stores and veterinary
clinics. The required foot soaking solution is 20% zinc
sulfate with a wetting agent (liquid laundry detergent)
added. A 20% solution is equal to 2 pounds of zinc
sulfate powder in one imperial gallon of water or 2 kg
of powder in 10 litres of water.
To calculate the capacity of the
the length by the width by the
imperial gallon equals 280 cubic
use the inside measurements of
calculating its capacity.
footbath, multiply
water depth. One
inches. Be sure to
the footbath when
For example, a footbath that is 16 feet long by 4
feet wide might have inside measurements of 189
inches by 45 inches. If it holds water to a depth of
three inches, the footbath would have a capacity of
(189x45x3)/280 = 91 gallons. This footbath would
require 182 pounds of zinc sulfate.
Add one cup of liquid laundry detergent to the foot
bath for every 30 gallons of solution, just over three
cups in this example. This acts as a wetting agent,
enabling the solution to adhere and penetrate into
the hooves.
The concentration of the solution must be checked
frequently, as it will be considerably less effective if
it drops below 15% zinc sulfate. Use a battery tester
(NOT an antifreeze tester) to monitor the solution.
Used zinc solution can be an environmental hazard
and should be disposed of on a manure pile where it
will be composted and diluted with organic material
before being spread on cropland.
This fact sheet was made possible by support from
DLFOA
Diversified Livestock Fund
Of Alberta Ltd.
Printed November 2007